The present invention relates generally to a tubular implantable prosthesis having a knitted textile structure. More particularly, the present invention relates to an endoprosthesis with a knitted textile structure having increased longitudinal stretchability.
An intraluminal prosthesis is a medical device used in the treatment of diseased blood vessels. An intraluminal prosthesis is typically used to repair, replace, or otherwise correct a diseased or damaged blood vessel. An artery or vein may be diseased in a variety of different ways. The prosthesis may therefore be used to prevent or treat a wide variety of defects such as stenosis of the vessel, thrombosis, occlusion or an aneurysm.
One type of intraluminal prosthesis used in the repair of diseases in various body vessels is a stent. A stent is a generally longitudinal tubular device formed of biocompatible material which is useful to open and support various lumens in the body. For example, stents may be used in the vascular system, urogenital tract and bile duct, as well as in a variety of other applications in the body. Endovascular stents have become widely used for the treatment of stenosis, strictures and aneurysms in various blood vessels. These devices are implanted within the vessel to open and/or reinforce collapsing or partially occluded sections of the vessel.
Stents generally include an open flexible configuration. This configuration allows the stent to be inserted through curved vessels. Furthermore, this configuration allows the stent to be configured in a radially compressed state for intraluminal catheter implantation. Once properly positioned adjacent the damaged vessel, the stent is radially expanded so as to support and reinforce the vessel. Radial expansion of the stent may be accomplished by inflation of a balloon attached to the catheter or the stent may be of the self-expanding variety which will radially expand once deployed. Structures which have been used as intraluminal vascular grafts have included coiled stainless steel springs; helically wound coil springs manufactured from a heat-sensitive material; and expanding stainless steel stents formed of stainless steel wire in a zig-zag pattern. Examples of various stent configurations are shown in U.S. Pat. Nos. 4,503,569 to Dotter; 4,733,665 to Palmaz; 4,856,561 to Hillstead; 4,580,568 to Gianturco; 4,732,152 to Wallsten and 4,886,062 to Wiktor, all of whose contents are incorporated herein by reference.
A graft is another commonly known type of intraluminal prosthesis which is used to repair and replace various body vessels. A graft provides a lumen through which blood may flow. Moreover, a graft is often configured to have porosity to permit the ingrowth of cells for stabilization of an implanted graft while also being generally impermeable to blood to inhibit substantial leakage of blood therethrough. Grafts are typically tubular devices which may be formed of a variety of materials, including textile and non-textile materials.
A stent and a graft may combined into a stent-graft endoprosthesis to combine the features thereof. The graft, however, in the stent-graft endoprosthesis should comply with the implantation requirements of the stent which often include collapsing the stent for placement at an implantation site and expansion of the stent for securement thereat. Grafts which cannot easily accommodate the longitudinal and/or radial dimensional changes from a unexpanded or collapsed state to an expanded stent often complicate the implantation of the stent-graft. For instance, some grafts are folded in the collapsed or unexpanded state and must be subsequently be unfolded to accommodate the expanded stent. The unfolding of the graft, however, often complicates the placement of the graft on the stent and the implantation of the stent-graft itself. Alternatively, noncontiguous grafts have been used with expandable stent-grafts. Upon expansion of the stent, however, portions of the noncontiguous graft often separate to accommodate the stent expansion. This separation leaves gaps in the graft structure thereby permitting the leakage of blood through these gaps.
Thus, there is a need for a graft that compliments the implantation of an expandable stent of a stent-graft endoprosthesis. In particular, there is need for a graft that is securably attached to the stent in both the expanded and unexpanded state without complicating the mechanical dynamics of the stent or the graft.
The present invention provides an implantable tubular prosthesis having a radially expandable tubular stent structure having a first diameter and capable of longitudinal expansion or contraction to achieve a second diameter which is different from the first diameter and a tubular knitted tubular graft circumferentially disposed and securably attached to the stent. The graft has a pattern of interlaced wale and course yarns in a knit pattern to permit longitudinal expansion or contraction of the graft substantially consistent with the longitudinal expansion or contraction of the stent.
The prosthesis of the present invention is capable of longitudinal expansion from 50 to 200 percent by length from a quiescent state. Alternatively, the prosthesis of the present invention is capable of 50 to 200 percent longitudinal contraction by length to achieve a substantially quiescent state from an unexpanded state. Furthermore, the textile graft of the present invention is substantially fluid-tight in its quiescent state.
To achieve such a degree of longitudinal expansion or contraction the textile graft includes a stretchable knit pattern. The pattern is a warp knitted pattern having a set yarns diagonally shifted over one or more yarns to form a loop between engaging yarns. Furthermore, the engaging yarns alternately form open loops where the engaging yarns do not cross over themselves and closed loops where the engaging yarns cross over themselves. The knit pattern is generally described as a Atlas or an modified-Atlas knit pattern. Such patterns depart a high degree of flexibility and stretchability to the textile graft of the present invention.
The knit pattern further includes a plurality of front and back yarns formed from single stitches, where the single stitches are deposed in a plurality of stitch repeating patterns. A first stitch has a repeating pattern traversing diagonally by two or more needle positions and a second stitch has a repeating pattern alternatively traversing diagonally by three or more needle positions and by one needle position.
In one aspect of the present invention an implantable tubular prosthesis capable of longitudinal expansion from a quiescent state to an elongated state in provided. The prosthesis includes a radially contractible and longitudinally expandable tubular stent having a quiescent diameter and quiescent length capable of longitudinal expansion to the elongated state having an elongated length and a contracted diameter, wherein the elongated length is greater than the quiescent length and the contracted diameter is smaller than the quiescent diameter, and further wherein the stent is capable of resiliently returning from the elongated state to the quiescent state. The prosthesis further includes a tubular knitted tubular graft circumferentially disposed and securably attached to the stent in the quiescent state. The graft has a pattern of yarns interlaced into stitches in a knit pattern capable of resilient longitudinal elongation and resilient radial contraction of the graft to the elongated state. Furthermore the graft has from 400 to 900 stitches per square centimeter to provide compliancy in the quiescent state.
In another aspect of the present invention an implantable tubular prosthesis capable of longitudinal expansion from a quiescent state to an elongated state includes a radially contractible and longitudinally expandable tubular stent as described above and a tubular knitted tubular graft having a warp knitted pattern of yarns forming a textile layer having an interior surface and an exterior surface, wherein interior yarns predominate the interior surface and form loops in the longitudinal direction of the prosthesis, and exterior yarns predominate the exterior surface and are diagonally shifted over one or more of the interior yarns in an alternating pattern along a width of the prosthesis to engage the interior yarns. The interior yarn alternately interlaces the engaging exterior yarn to form open loops where the interior yarn does not cross over itself and closed loops where the interior yarn does cross over itself
In another aspect of the present invention an implantable tubular prosthesis capable of longitudinal expansion from a quiescent state to an elongated state includes a radially contractible and longitudinally expandable tubular stent and a tubular knitted tubular graft circumferentially disposed and securably attached to the stent in the quiescent state, where the graft has greater than about 350 stitches per square centimeter in its knit pattern to provide compliancy of the graft and wherein the prosthesis is capable of longitudinal expansion from 50 to 200 percent by length.
In yet another aspect of the present invention, an implantable tubular prosthesis capable of longitudinal expansion from a quiescent state to an elongated state includes a radially contractible and longitudinally expandable tubular stent and tubular knitted tubular graft circumferentially disposed and securably attached to the stent. The graft has a knit pattern with greater than about 350 stitches per square centimeter while also having a wall thickness from about 0.3 to about 0.4 millimeters.
In still another aspect of the present invention, an implantable tubular prosthesis capable of longitudinal expansion from a quiescent state to an elongated state includes a radially contractible and longitudinally expandable tubular stent and tubular knitted tubular graft circumferentially disposed and securably attached to the stent, wherein the stent and the graft are resiliently deformable between the quiescent and elongated states and further wherein the graft non-bulgingly contracts from the elongated state to the quiescent state to circumferentially abut the stent.
In still yet another aspect of the present invention, an implantable tubular prosthesis capable of radial expansion from a quiescent state to a radially expanded state includes a radially expandable and longitudinally contractible tubular stent and a tubular knitted tubular graft circumferentially disposed and securably attached to the stent in the quiescent state. The graft has a pattern of yarns interlaced into stitches in a knit pattern capable of resilient radial expansion and resilient longitudinal contraction of the graft to the elongated state and has from 400 to 900 stitches per square centimeter to provide compliancy for the graft in the quiescent state.
In other aspects of the present invention, a non-textile, desirably ePTFE, layer is provided with the endoprosthesis of the present invention. Moreover, a textile graft capable of resilient elongation and having from 400 to 900 stitches per square centimeter is provided. Furthermore, an implantable medical fabric is provided. The medical fabric is a knitted textile with a high degree of stretchability because of the Atlas and the modified-Atlas stitches used to form the fabric. A method for producing the high stretch knit prosthetic device is also provided.